1. Field of the Invention
The present invention relates to an apparatus for controlling injection of fuel into an engine and an apparatus for controlling combustion in an engine, and in particular, to the apparatuses in which the injection includes a preliminary sub Injunction preceding a main injection for producing the output torque in the engine and being less in an fuel amount to be injected than the main injection.
2. Description of the Related Art
An engine (internal combustion engine) is used as a power source in automotive vehicles. In this engine, fuel injected by fuel injection valves (for example, injectors) is ignited for combustion, so that output torque is generated from the engine.
Recently, in a diesel engine for vehicles, an injection technique, called multiple-step injection, has been put to practical use. In the injection based on this technique, a preliminary sub injection is carried out before the main injection primarily that produces the output torque of the engine during each combustion cycle. This preliminary sub injection is designed to inject a smaller amount of fuel than that of the main injection. That is, the fuel amount in the preliminary sub injection is part of the whole amount of fuel to be injected per combustion cycle. This preliminary sub injection is called “pilot injection.” When being performed, this pilot injection generates heat in the combustion chamber of each cylinder to warm the inner wall thereof. Thus, with the wall thereof sufficiently heated, the main injection is performed, thus reducing delay in the ignition of the main injection, thus suppressing combustion noise due to the ignition delay. Therefore, the diesel engine is able to provide improved running operation in a lower-speed and lower-load running range which appears in an idling operation, for instance. Additionally, the fuel injection is divided between the pilot injection and the main injection, which results in that a premixing amount of fuel is reduced and a certain amount of air-fuel mixture is burned in the initial combustion. The combustion gas is thus kept at lower temperatures, which makes partly suppresses the initial combustion of the main injection and reduces the emission of NOx (nitrogen oxide) from the engine.
However, there is a problem that the effect of the pilot injection is liable to changes in the environmental conditions, because the pilot injection needs only a minute amount of fuel. To cover this difficulty, a map is prepared beforehand in a memory device and optimum injection patterns are written for every engine operating state. For preparing this kind of map, experiments and/or simulations are conducted to obtain such optimum injection patterns. Reference is made to this map to set an appropriate injection patter depending on each engine operating state.
However, it will take a larger amount of labor (in man-hours) to make such maps (called the “matching map”), prolonging the work and increasing manufacturing costs. Further, the matching map is not able to follow changes in the characteristics of the engine which will probably occur with long use of the engine. That is, with an increase in the use time, the memorized injection patterns will deviate from optimum injection patterns to the current engine conditions. If this happens, the combustion amount and combustion temperature of fuel in response to the pilot and main injections will be shifted from their reference values. The combustion timing is also subjected to a shift, giving rise to a deteriorated emission quality and unstable combustion states.
In consideration of this difficulty, Japanese Patent Application Laid-open Publication No. 2004-100559 discloses an apparatus in which CPS (cylinder pressure sensor) is used to detect the cylinder pressure during the operation of an engine and this pressure is used to calculate combustion parameters for the combustion start timing and other timings. The calculated combustion parameters are then used to adjust the fuel amount and timing of the pilot injection.
However, the apparatus according to the foregoing conventional publication is still confronted with a drawback. This results from the fact that the amount injected by the pilot injection is minute. When burned, the minute fuel amount will cause only small changes in the cylinder pressure, with the result that it is considerably difficult to detect combustion states in response to such pressure changes Additionally, the CPS is generally expensive, and being disadvantageous in reducing the whole manufacturing costs of the apparatus.